SNAP output for PDB entry 8b0r [SNAP web server]

PDB-id

8b0r; SNAP-derived features in text and JSON formats; DNAproDB

Class

hydrolase

Method

X-ray (2.2 Å)

Summary

Structure of the calpl-ca4 complex

Reference

Rouillon C, Schneberger N, Chi H, Blumenstock K, Da Vela S, Ackermann K, Moecking J, Peter MF, Boenigk W, Seifert R, Bode BE, Schmid-Burgk JL, Svergun D, Geyer M, White MF, Hagelueken G (2023): "Antiviral signalling by a cyclic nucleotide activated CRISPR protease." Nature, 614, 168-174. doi: 10.1038/s41586-022-05571-7.

Abstract

CRISPR defense systems such as the well-known DNA-targeting Cas9 and the RNA-targeting type III systems are widespread in prokaryotes_1,2. The latter can orchestrate a complex antiviral response that is initiated by the synthesis of cyclic oligoadenylates (cOAs) upon foreign RNA recognition_3-5. Among a large set of proteins that were linked to type III systems and predicted to bind cOAs_6,7, a CRISPR associated Lon protease (CalpL) stood out to us. The protein contains a sensor domain of the SAVED (SMODS-associated and fused to various effector domains) family₇, fused to a Lon protease effector domain. However, the mode of action of this effector was unknown. Here, we report the structure and function of CalpL and show that the soluble protein forms a stable tripartite complex with two further proteins, CalpT and CalpS, that are encoded in the same operon. Upon activation by cA₄, CalpL oligomerizes and specifically cleaves the MazF-homolog CalpT, releasing the extracytoplasmic function (ECF) sigma factor CalpS from the complex. This provides a direct connection between CRISPR-based foreign nucleic acid detection and transcriptional regulation. Furthermore, the presence of a cA₄-binding SAVED domain in a CRISPR effector reveals an unexpected link to the cyclic oligonucleotide-based antiphage signaling system (CBASS).